A tunnel kiln is an elongated kiln or oven normally made of refractory material, through which ware such as brick, tile and like material may be continuously processed and transported as it is subjected to desired heating conditions. The ware is commonly transported through a tunnel kiln on flatbed ware cars which roll on rails extending through the length of the tunnel. The kiln is normally operated so that the tunnel is full of ware cars bumper to bumper. At certain intervals a new car is pushed into the entrance of the tunnel thereby ejecting a fully processed car of ware from the exit of the tunnel.
Tunnel kilns are commonly divided into successive zones or sections in which the temperature, atmospheric conditions and air circulation can be controlled to effect efficient heat treatment. These sections include a preheating section, a firing section and a cooling section. The maximum temperature of the kiln is found in the firing section. The heat for the preheat section is supplied primarily by the hot gases drafted from the firing section. Supplementary heat is added by booster burners positioned in the preheat section. Angled baffles with pivotable dampers are positioned within the preheat section in the path of the hot exhaust gas to distribute the hot gases as desired throughout the preheat section. In this manner the desired degree of preheat can be controllably applied in a uniform way through the preheat section.
The chief advantage of a tunnel kiln resides in the fact that the ware is processed continuously with a counter-current flow to the exhaust, thereby yielding excellent fuel efficiency and a high volume of production with a minimum of handling of the ware. The present invention takes advantage of the benefits of current tunnel kiln designs to process and separate co-mingled metals into their distinct constituents.